Fatigue limit prediction of large scale cast aluminum alloy A356

Casting defects such as gas pores and shrinkages typically occur during casting process. These casting defects affect fatigue crack initiation and strongly dominate fatigue strength. Particularly, in a large scale component, the molten metal flow is complicated and the cooling rate is dependent on the locations, which affect the formation of casting defects. In the present study, rotating bending fatigue tests of cast aluminum alloy A356 were conducted using the specimens sampled at three locations of a large scale component where the cooling rates were different. The fatigue limit was predicted based on the statistics of casting defect size and compared with the experimental results. Fractographic analyses revealed fatigue crack initiated from casting defect in all specimens. Murakami et al. suggested the method for predicting the fatigue limit of steel using the extreme value statistics of inclusion size (Murakami et al., 1989). Ueno et al. modified Murakami's equation and proposed the equations to predict the fatigue limit of die-cast aluminum alloy based on the defect size (Ueno et al., 2012). The present authors suggest the modified evaluation method of defect size considering the combination of the neighboring defects which exist near to each other. The predictions agree well with the experimental results but they are slightly different, which indicates the other metallurgical factors affect fatigue strength. (C) 2014 Elsevier Ltd.